The first weather report on two brown dwarfs – celestial bodies larger than planets but smaller than stars – closer to us has just been produced.
The weather there is inclement, to say the least: incredibly hot, with a toxic cocktail roaming the atmosphere and with clouds of silicate particles close to Saharan sandstorms.
Researchers used records from the James Webb Space Telescope to conduct a detailed survey of atmospheric conditions in brown dwarfs, specifically a pair that orbits about six light-years from Earth, a measurement considered close on a cosmic scale. A light year is the distance it takes light to travel in one year, that is, 9.5 trillion kilometers.
The information collected by Webb provides a three-dimensional view of how the climate changes during the brown dwarf’s rotation – the larger of the two taking seven hours and the smaller five – with multiple cloud layers found at different atmospheric depths.
The atmospheres of the two brown dwarfs are dominated by hydrogen and helium, with small amounts of water vapor, methane and carbon monoxide. The temperature in its clouds reaches a maximum of 925 ºC, a value similar to a common candle flame.
“In this study, we have created the most detailed weather map of any brown dwarf ever seen,” said astronomer Beth Biller of the Institute of Astronomy at the University of Edinburgh, lead author of the study published on Monday (15) in the academic journal Monthly Notices, of the Royal Astronomical Society.
Brown dwarfs are neither star nor planet, but something in between. They emit their own light thanks to the heat they possess, “just like you can see a reddish coal because of how hot it is,” said Biller. It is this light that researchers investigated with Webb. Unlike stars, brown dwarfs do not have nuclear fusion in their cores.
“Like planets, but unlike stars, brown dwarfs also have clouds that are made of precipitates in their atmospheres. It turns out that, even though there are water clouds on Earth, the clouds of brown dwarfs are much hotter and probably made of hot silicate particles, something like a very hot sandstorm in the Sahara,” said Biller.
The current scientific consensus is that brown dwarfs formed from large clouds of gas and dust like stars, but are not massive enough to undergo nuclear fusion. Its composition is similar to gigantic gas planets like Jupiter, the largest in our solar system. Its mass is up to 80 times greater than that of Jupiter. Just for comparison, the mass of the sun is about 1,000 times greater than that of Jupiter.
The two brown dwarfs analyzed by Webb formed about 500 million years ago. Each of them has a diameter comparable to Jupiter, but one is 35 times larger than Jupiter and the other is 30 times larger.
Brown dwarfs are relatively common. About a thousand are known, compared to more than 5 thousand exoplanets. Webb examines the cosmos primarily using infrared, while the Hubble telescope, its predecessor, analyzed optical and ultraviolet waves.
“The atmospheres of brown dwarfs are highly complex. Webb provides a huge leap forward in our ability to understand them by providing unprecedented sensitivity and wavelength range,” said astronomer and study co-author Johanna Vos of Trinity College in Dublin, Ireland.
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